Nonlinear optical dyes (organic molecules having large nonlinear polarizabilities) have been recognized as potentially useful as components of the optical elements in optical frequency converters and in electrooptic devices. Japanese Patent Application 2/118,524 for example, describes the use of (thio)barbituric acid containing compounds as NLO dyes. Generally, in order for the NLO dyes to exhibit the large second order optical susceptibilities essential to nonlinear optic applications, the molecules must be constructively arrayed in a noncentrosymmetric configuration. Some molecules have been crystallized in a noncentrosymmetric space group, but this method does not work for all potentially useful molecules, and the resulting shape and properties are limited by the very nature of a crystal.
Certain NLO dyes have been used, for example, in combination with glassy polymers to provide nonlinear optical elements. The choice of the dye molecule and glassy polymer affects the stability of nonlinear optical effect obtained, because the aligned dye molecules have a tendency to "relax" over time, thereby losing the alignment necessary for the enhanced nonlinear optical properties.
NLO groups based on some NLO dye moieties have been used as side groups for polymers such as polyacrylics and polystyrenes to provide polymers for use in NLO devices. See for example WO 91/03504, which describes such acrylic polymers. Polymers which have relatively high glass transition temperatures are considered particularly useful.